Forgive me if i'm wrong, but is it not the case that the interest rate you receive from putting your money in a bank account is basically your share of the profit that they make from investing it?

Other than that, i agree with the sentiment - if you have time and enough capital, invest it yourself. If not, put it in the bank and they'll invest it for you, and take some of the proceeds - you'll get a smaller return but considering you did literally none of the work, seems like quite a good deal to me. :)